In the field of lighting devices, in particular LED units for offline applications such as retrofit lamps, solutions are demanded to cope with high efficiency, high power density, long lifetime, high power factor, low costs and different supply voltages among other relevant features. Various LEDs tubes (TLED) are used to replace fluorescent (TL) lamps as a retrofit lamp. Most of the TL (T8) lamps are driven by high frequency ballasts, wherein either instant start or programmed start ballasts are used. The program start ballasts preheat the filament before ignite the lamp in order to enlarge the lifetime while the instant start ballasts does not provide filament heating. Therefore, retrofit LED lamps have to be adapted to different drive voltages.
In order to operate the retrofit LED lamp properly, most of the retrofit LED lamps require a rewiring of the fluorescent lamp, i.e. by bypassing the ballast. This is complicated and requires a fixture of the present driver circuit. The most desirable way is to replace the fluorescent lamp directly by the LED tube without changing anything and by connecting the input terminals of the LED lamp with the high frequency ballast output terminals. However, this direct replacement leads to large power loss in the ballast and reduces the efficiency of the lamp.
A further demand of TLED retrofit lamps is to prevent electrical shocks when the TLED lamp is fixed. To avoid electrical shocks due to an electrical contact of the input terminals to external connection terminals, it is widely used to disconnect the connection terminals at one end of the TLED so that no electrical conductive path is provided from one end to the other. However, this pin safety solution requires a rewiring of the fluorescent lamp fixture including the above-mentioned disadvantages.
From WO 2013/024389 A1 an electronic ballast-compatible lighting driver for light emitting diode lamps is known having a rectifier for connecting the driver to the ballast and for providing a rectified voltage for driving the LED unit. However, since the driver device is only connectable to an existing ballast, the power loss of the ballast reduces the efficiency of the lighting unit in general.
From US 2010/0201270 A1 a diode light tube and an AC switching power supply is known having two separate input connections to connect different AC power supplies to the diode, wherein the connection terminals for the different power supplies are connected to separate rectifier units in order to provide a DC voltage for powering the load. The disadvantage of the driver device known from this document is that the technical effort due to the separate rectifier units is increased and that an electrical connection is provided between the different input terminals so that the risk of electrical shocks is present and a separate pin safety is necessary.
WO2009/136322 discloses a connection circuit for connecting a driver device of a LED unit to a power supply, which circuit is provided with first and second input terminals and a rectifier unit. Both the first and the second input terminal are directly connected to the rectifier. The connection of the first terminal with the rectifier unit on the one hand and the connection of the second terminal with the rectifier on the other hand are bridged by a capacitor. This connection circuit is suitable for use in fixture with ballast however is not suitable for connection with other power supplies. Moreover, safety is not guaranteed when the connection circuit is connected in an unsuitable fixture or when improper used.